Session Initiation Protocol (SIP) is an open signaling protocol for establishing many kinds of real-time communication sessions. Examples of the types of communication sessions that may be established using SIP include voice, video, and/or instant messaging. These communication sessions may be carried out on any type of communication device such as a personal computer, laptop computer, Personal Digital Assistant, telephone, mobile phone, cellular phone, or the like. One key feature of SIP is its ability to use an end-user's Address of Record (AOR) as a single unifying public address for all communications. Thus, in a world of SIP-enhanced communications, a user's AOR becomes their single address that links the user to all of the communication devices associated with the user. Using this AOR, a caller can reach any one of the user's communication devices, also referred to as User Agents (UAs) without having to know each of the unique device addresses or phone numbers.
Voice over Internet Protocol (VoIP) is a general term for a family of transmission technologies used to deliver voice communications over IP networks such as the Internet or other packet-switched networks. Other terms frequently encountered and synonymous with VoIP are IP telephony, Internet telephony, voice over broadband (VoBB), broadband telephony, and broadband phone.
VoIP systems employ session control protocols, such as SIP, to control the set-up and tear-down of calls as well as audio codecs which encode speech allowing transmission over an IP network as digital audio via an audio stream. The advantage to VoIP is that a single network can be utilized to transmit data packets as well as voice and video packets between users, thereby greatly simplifying communications.
Security is critical to the reliable and protected exchange of information when communicating over IP networks. In a VoIP network, signaling and media security is established hop-by-hop on both the signaling plane and on the media plane. Although it is possible to establish end-to-end secure calls, when the call traverses non-VoIP paths or egresses outside the enterprise administrative domain, it is not apparent whether the hop-by-hop security policies of the enterprise have been maintained. Thus, the participants of the call cannot be sure that their conversation is secure.